Agricultural vehicles have long been provided with hitches for coupling various implements to the vehicle, whereby the implement may be moved through a field by a vehicle and an operation performed upon the soil of the field or a crop growing thereon.
A type of hitch in frequent use is the three-point hitch, adjustable in the height at which it carries an implement so that the depth of engagement of an implement with the soil may be adjusted and so that the implement may be raised up out of engagement with the soil when the vehicle is turning around at the end of a row, or when the vehicle is transporting the implement to or from the field, often over a paved road.
Since it is difficult to align a vehicle to an implement when backing up the vehicle to the implement for the purpose of mounting the implement upon the hitch, hitches are necessarily designed with a capability of lateral movement, or "sway", so that they can be swung to either side to complete the alignment when the vehicle has been drawn sufficiently near the implement to couple it. To make the aligning and coupling process as easy as possible, the amount of lateral movement available, or width of sway, may be unimpeded and restricted only by the geometries of the vehicle, the implement, and the hitch itself.
Conversely, when the hitch is raised by the vehicle for carrying the implement to or from the field or for making a sharp turn at the end of a row, it is desirable for there to be no sway (i.e., for the hitch and therefore the implement to be held against lateral movement) so that normal movement of the vehicle in motion will not allow the implement to randomly swing to and fro, swinging into objects otherwise cleared by the vehicle and swinging into a rear wheel, or crawler tread, of the vehicle itself. For this reason, hitches often include sway limiting devices which can be adjusted to "full sway" or "no sway" positions, although such adjustments sometimes require the use of tools such as wrenches and therefore necessitate that the vehicle operator keep tools of the proper sizes at hand.
It is desirable for an implement hitch to have another position of sway adjustment, a "partial sway" position which provides sufficient width of sway to allow a tilling implement such as a plow to briefly move aside without overstressing the hitch or pulling laterally on the rear of the vehicle when encountering an obstacle such as a large stone, or to allow a soil surface engaging implement to follow contours of the soil surface without imposing undue loads upon the vehicle or its hitch. Such position adjustments are generally configured to limit sway to a narrow enough width that the hitch or the implement cannot swing laterally far enough to come into contact with the rear wheels or treads of the vehicle.
Many wheeled vehicles are provided with an adjustable rear tread width; i.e., the rear wheels may be moved to positions nearer a longitudinal centerline of the vehicle and the vehicle thereby provided a narrower rear tread width desirable for particular operations and particular crop row spacings. The wheels are otherwise generally adjusted to outermore positions for best stability and handling of the vehicle. When they are in their innermore positions for a narrower tread width, however, the normal "partial sway" position of sway adjustment may not sufficiently limit the width of sway, and the implement or hitch may strike one or both of the tires mounted upon the wheels. This may cause damage to the tires, the hitch, and/or the implement.